This application claims the priority of Japanese Patent Application No. 10-195463 filed on Jul. 10, 1998 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an imaging device for an endoscope, and more particularly, it relates to the composition of an endoscope system which can display a picture imaged by using one scope, by either system selected from the NTSC system and the PAL system.
2. Description of the Prior Art
In FIG. 3, one example of the composition of a conventional electronic endoscope is shown, and as shown in the figure, for example, on the scope side, a timing generator 2 is connected to a CCD 1 which is a solid imaging element. To this timing generator 2, a crystal oscillator 3 for the NTSC (television) system is connected, and various types of drive signals with specified frequencies are formed by using, for example, a signal with a frequency of about 14.32 MHz oscillated in this oscillator 3, and this is given to the CCD 1.
To the CCD 1, an AGC (automatic gain control) circuit including a CDS (correlative double sampling) circuit is connected, and to this AGC circuit 5, a DSP (digital signal processor) 7 is connected through an A/D converter 6. Then, a first CPU 8 for controlling these circuits is provided.
On the other hand, on the side of the PAL processor to which the scope is connected, at the position where the signal outputted from the DSP 7 is inputted, a memory section 10 equipped with an imaging memory 10A and a display memory 10B is provided, and to the rear stage of this memory section 10, a D/A converter 11 is connected.
Furthermore, a second CPU 12 for controlling these circuits, a PAL system oscillator 13 for outputting, for 15 example, an oscillating signal with a frequency of about 17.73 MHz, and a ROM 14 (read only memory) are provided, and a synchronization signal formed on the basis of the PAL oscillating signal is given to the memory 10. Furthermore, in the ROM 14, the information to make the scope side (the first CPU 8) recognize that the processor is a PAL system processor is stored.
According to an electronic endoscope composed like this, when an oscillating signal with a frequency of about 14.32 MHz is inputted into the timing generator 2 from the oscillator 3 of the NTSC system, a horizontal synchronization signal fh1 with a frequency of 15.734 kHz vertical synchronization signal fv1 with a frequency of 59.94, Hz, a horizontal CCD drive pulse and a vertical pulse are formed from the oscillating signal in this generator 2, and these are outputted to the CCD 1.
In this CCD 1, a picture signal is read out on the basis of each of the synchronization signals, and this picture signal is converted into a digital signal to be supplied to the DSP 7 after specified amplification, sample hold, and the like have been performed in the CDS/AGC 5. In this DSP 7, gamma processing and the like are performed, and the output of this DSP 7 is sent to the memory section 10 on the processor side.
In this memory section 10, the picture signal is once written in the imaging memory 10A in the timing of the NTSC system, but when reading out the signal, the signal is read out on the basis of the PAL system synchronization signal, that is, a horizontal synchronization signal fh2 with a frequency of 15.625 kHz and a vertical synchronization signal fv2 with a frequency of 50 Hz, and this picture signal is stored in the display memory 10B. Accordingly, while shifting from the imaging memory 10A to the display memory 10B, the conversion to the PAL picture data is performed. By the way, the horizontal synchronization signal fh2 and the vertical synchronization signal fv2 are formed by the second CPU 12 from the output of the oscillator 13.
After that, the picture signal read out from the display memory 10B is converted into an analog signal at the D/A converter 11, and this signal is outputted to a PAL monitor through a specified processing circuit, and a picture in an observed object is displayed on the PAL monitor. By the way, in the case where a picture is displayed by the NTSC system, an NTSC system processor is connected to the scope.
However, in an electronic endoscope system of converting from the NTSC system to the PAL system, the frequencies of the synchronization signals are different as mentioned above, and therefore, there is such a problem that the conversion screen flickers especially in the case where the observed object moves. This is caused by the reason that there is a difference between the write-in speed and the read-out speed to the imaging memory 10A of the memory section 10 and the write-in speed depends on the horizontal synchronization signal and the vertical synchronization signal of the NTSC system and the read-out speed depends on the horizontal synchronization signal and the vertical synchronization signal of the PAL system.
In FIG. 4, the difference between the picture display processing of the NTSC system and the picture display processing of the PAL system is shown, and the number of scanning lines is 525 in the NTSC system but in the meantime, the number is 625 in the PAL system, and furthermore, the cycle of the horizontal synchronization signal is 15.734 kHz in the NTSC system but the cycle is 15.625 kHz in the PAL system, and consequently, there is a difference of t1=1/(15.625xc3x97103) xe2x88x921/(15.734xc3x97103). Accordingly, in the data of 1 field (or 1 frame), the write-in speed in the NTSC system is faster than the read-out speed in the PAL system, and in the course of 1 field, the data of the next field with a time difference is mixed, and eventually, a flicker of the screen is caused in the picture with movement or the like.
Furthermore, the PAL system processor described in FIG. 3 is produced separately from the NTSC system processor, and consideration for the difference of the power source or the like is also necessary, but it is a convenience if at least the signal processing processor section can be one circuit composition regardless of the difference of the system.
The present invention is made due to the above problems, and it is an object thereof to provide an imaging device for an endoscope equipped with both the NTSC system and the PAL system in which it is possible to restrain the flicker of the screen caused when converting the television system, and further, in which it is possible to unify the processor circuit for performing the display processing of different systems.
In order to attain the above object, the present invention comprises: a scope for capturing an observed object; an imaging element suitable for the number of scanning lines of either the NTSC system or the PAL system for imaging the picture of the observed object; an oscillator for the NTSC system and an oscillator for the PAL system; a drive means which selects either of both the oscillators and drives the imaging element on the basis of the timing signal corresponding to each selected system; and a picture processing processor which processes the picture signal outputted from the imaging element to selectively form a picture of the NTSC system and a picture of the PAL system.
In the picture memory arranged in the picture processing processor, the frequency of the horizontal synchronization signal when writing in the picture signal obtained in the imaging element and the frequency of the horizontal synchronization signal when reading out the picture signal are conformed.
Furthermore, the PAL oscillator can be an oscillator to generate a frequency of N times about 15.625 kHz near the frequency of the horizontal synchronization signal for the NTSC.
Moreover, it is preferable to arrange the oscillator for the NTSC system and the oscillator for the PAL system in the scope when the imaging element is arranged in the scope and to arrange them onto the mounting member of the imaging element when the imaging element is connected to the eyepiece portion of the scope.
According to the above composition, the oscillator for the NTSC system and the oscillator for the PAL system are selectively used on the scope side, and when the NTSC system is selected, the picture data is extracted from the imaging element by the horizontal synchronization signal with a frequency of 15.734 kHz. Usually, as this imaging element, a CCD having a number of horizontal lines suitable for the NTSC system is used, and on the processor side, the synchronization signal with the above frequency is also used, and therefore, in this case, the picture display processing is performed without question similarly to the previous processing.
On the other hand, when the PAL system is selected, the picture data is extracted from the CCD by the horizontal synchronization signal with a frequency of 15.625 kHz formed by the oscillator for the PAL system, and this picture data is stored in the memory on the processor side in the same timing. After that, from this memory, the picture data is read out by the horizontal synchronization signal with a frequency of the above PAL system, and at this moment, the conversion and expansion (compression) of the scanning line data for converting the number of scanning lines from 525 to 625 is performed.
According to this, the vertical synchronization term and the horizontal synchronization term in the write-in and the read-out to and from the memory (for conversion) are the same, and the time difference between the write-in and the read-out in 1 field (or 1 frame) becomes small, and the flicker of a screen is eliminated.